The present invention relates generally to color management in projection displays and similar systems, and more particularly to skew-ray correction in the color management of video projection systems.
It is generally desirable for projection systems to produce high quality images while being compact and inexpensive. In prior art transmissive systems using polysilicon liquid crystal panels, high contrast is achieved by situating each panel between crossed sheet polarizers. Color management beamsplitters/combiners and other optics are external to these units, insuring that polarization is not contaminated and contrast degraded.
In projection systems using reflective panels, such as liquid crystal on silicon (LCOS) displays, beam routing is frequently accomplished using polarizing beamsplitters (PBSs). PBSs are four-port devices, comprising an input port, an output port, and a reflective panel port, with the fourth port typically unused. The behavior of thin-film PBS cubes, for instance, is such that s-polarized light is reflected, while orthogonally polarized light is substantially transmitted.
Efficient use of ultra-high pressure mercury (UHP) lamp emission to achieve high-brightness generally requires that the projection system operate at f2.8 or lower. F-number reduction to achieve high brightness is often accompanied by diminished contrast ratio. In practice, precise separation of input and modulated light becomes challenging when PBSs are used in even modest f-number systems. The control of skew rays in such systems has previously been analyzed in the context of contrast ratio preservation. A simple quarter-wave retarder between the panel and PBS is a well-known compensation scheme for managing contrast loss due to the PBS geometrical rotation.
Compact LCOS-based projection systems can be realized by combining the beam separation function of the PBS with a polarization based color management. Retarder stacks, as described in U.S. Pat. No. 5,751,384, enable encoding of color by polarization, thereby expanding the role of neutral PBSs to function as color splitters and combiners. However, such color management systems have the same skew-ray susceptibility found in the panel ports. In order to maintain high color quality and contrast in low f-number systems, the polarization encoding incorporates skew ray correction.
An aspect of the invention is to provide an optical filter including at least three retarders where the at least three retarders cause optical rotation to light of a first spectrum substantially without introducing retardation.
An aspect of the invention is to provide an optical filter including at least three retarders wherein the at least three retarders act as a half wave plate to light of a first spectrum and wherein the at least three retarders act as a half wave plate with axcfx80/4 displaced optical axis to light of a second spectrum.
An aspect of the invention is to provide an optical filtering method, the steps of the method including optically rotating light of a first spectrum without introducing retardation.
An aspect of the invention is to provide an optical filter method, the steps of the method including retarding light of a first spectrum and retarding light of a second spectrum. A half wave of retardation is provided by the retarding light of a first spectrum and a retardation equivalent to a half wave plate with a xcfx80/4 displaced optical axis is provided by the retarding light of a second spectrum.
An aspect of the invention is to provide an optical arrangement including a half waveplate and a pair of beam splitters oriented orthogonally to each other. The pair of beam splitters sandwiching the half waveplate.
An aspect of the invention is to provide a method of filtering light, steps of the method including splitting a first light beam to form a second light beam, retarding the second light beam with a half wave of retardation to form a third light beam, and splitting the third light beam.
An aspect of the invention is to provide an optical arrangement including a planar polarizer, a beam splitter, and an out-of-plane retarder between the planar polarizer and the beam splitter.
An aspect of the invention is to provide a method of filtering light, the steps of the method including polarizing an incident light beam to form a polarized light beam, retarding the polarized light beam with an out-of-plane retarder to form a retarded light beam and splitting the retarded light beam.
An aspect of the invention is to provide a compensating color selective polarization filter (CCSPF) which, substantially independent of input polarization angle, has no effect on the state of polarization (SOP) of one portion of the spectrum, while another portion of the spectrum is converted to the orthogonal SOP.
Another aspect of the invention is to provide a CCSPF which reflects the SOP of one portion of the spectrum about an axis, while another portion of the spectrum is reflected about an axis displaced by xc2x1xcfx80/4 with respect to the aforementioned axis.
Another aspect of the invention is to provide a CCSPF which includes an out-of-plane uniaxial compensator.
Another aspect of the invention is to provide a skew ray compensated structure, including a first beam splitter, a second beam splitter, and a CCSPF. The CCSPF is between the first and second beam splitters, such that the SOP of skew rays transmitted by the first beam splitter are preconditioned so as to compensate for the skew-ray polarizing properties of the second beam splitter.
Another aspect of the invention is to provide a projection system including at least one structure comprising of a pair of beamsplitters bounding a CCSPF.
Another aspect of the invention is to provide a projection system including a pre-polarizer adjacent to a first CSPF that converts one spectrum of light to the orthogonal SOP, and does not change the SOP of another spectrum of light, a first PBS adjacent to the first CSPF for separating the one spectrum of light from the another spectrum of light, a second PBS adjacent to the first PBS, and a first display panel for selectively reflecting light adjacent to the second PBS, a first CCSPF between the first PBS and a third PBS that reflects the SOP of a first portion of the another spectrum of light about an axis and reflects the SOP of a second part of the another spectrum of light about another axis, a second panel for selectively reflecting light adjacent to a face of the third PBS opposing the first CCSPF, a third panel for selectively reflecting light adjacent to another face of the third PBS, a second CCSPF adjacent to a face opposing the third panel, the second CCSPF reflecting the SOP of the first portion of the another spectrum of light about an axis and reflecting the SOP of the second part of the another spectrum of light about another axis, a first half wave plate between the second PBS and the fourth PBS, a second CSPF that converts the SOP of one spectrum of light to the orthogonal state and does not effect the another spectrum of light adjacent to the fourth polarizing beam splitter, and a polarizer adjacent to the second CSPF.